Basically a rotary fluid compressor performs the steps of drawing in, compressing and pushing out fluid by means of a motor driving an eccentric shaft, letting a revolving part engage with a stator. In order to allow for a proper relative movement of the revolving part and the stator, an Oldham ring is used to ensure a circling movement of the revolving part around the stator's center without the revolving part rotating itself. When the revolving part circles around as driven by the eccentric shaft, it will move to and fro gliding along the Oldham ring's transverse axis. At the same time the Oldham ring carries out a longitudinal movement back and forth along a gliding path of the frame, in accordance with the revolving part's displacement.
As shown in FIGS. 8 and 9, a conventional Oldham ring 4 is a ring that is mounted between the revolving part and the frame 5. It performs a movement back and forth separately against the revolving part and the frame. While it moves back and forth, in order to prevent the revolving part and the frame from interfering with the fastening device 6 used to attach other machine elements, the frame's 5 outer diameter has to be increased, such that the fastening device 6 will not collide with the movement back and forth of the Oldham ring 4. Then, in order to accommodate the larger outer diameter of the frame 5, the size of the compressor's housing has to be enlarged and the compressor cannot be built compact.
On the Oldham ring 4, gliding parts 7 for the movements back and forth glide against the revolving part and the frame 5 to prevent the revolving part from rotating. The gliding parts 7 almost act like seals, so lubricating oil between the Oldham ring 4 on the one hand and the revolving part and the frame 5 on the other hand cannot be taken in by the fast moving gliding parts 7. This causes oil pressure, leading to impaired oil flow and energy loss.